Mechanical relaxation in poly(2.6‐dimethyl‐1.4‐phenylene oxide) in the glassy state

Dynamic mechanical properties (sound velocity, v, and damping factor, Q−1) have been determined in poly(2.6‐dimethyl‐1.4‐phenylene oxide) over a wide range of temperature (from 80 to 500°K) at acoustic frequencies. The examined polymer exhibits two mechanical relaxation effects, one, α, at temperatures above 480°K, characterized by a sudden strong drop of the elastic modulus and by a rapid increase of the damping factor with increasing temperature, and another, β, below the glass transition point, Tg, characterized by a small drop of the elastic modulus, between 290 and 370°K, and by a damping maximum at about 370K (fm = frequency corresponding to the maximum ⋍ 7000 Hz). The α relaxation effect has been attributed to the thermal excitation of cooperative motions in the chain, while the secondary β relaxation has been interpreted as due to oscillation of aromatic rings around COC bond. The damping maximum, for the lateer, is shifted toward higher temperatures with increasing frequency, following an ARRHENIUS‐type equation with an apparent activation energy of about 20 kcal/mole.